An inert gas, such as argon, is often used during welding to isolate and protect the molten metal of the weld from atmospheric gases. Materials in a molten state often react with gases in the atmosphere and become porous or brittle, reducing the quality of a weld formed with the material. For example, titanium will become brittle when exposed to atmospheric gases at temperatures over 1200.degree. F. During welding, the weld pool and a portion of the weld near the weld site typically have a temperature at which the material is susceptible to contamination by atmospheric gases. For adequate protection against contamination, the molten metal of the weld should be covered with an inert gas.
Various gas shielding devices are available for shielding the molten metal of a weld from atmospheric gases. U.S. Pat. No. 3,875,364 discloses a trailer shield for shielding the wake of the weld where the weld puddle, electrode tip and the arc of the welding torch are shielded by a stream of inert gas flowing from the shielding cup. Since the stream provided by the trailer device is separate from that of the cup, the molten metal between the trailer shielding device and the cup may be exposed to atmospheric gases at a temperature which results in contamination of the weld.
More complete protection for the weld material may be obtained by joining the trailer shield to the welding torch. Gas shielding devices which include a primarily shield section and a trailer shield section are shown in U.S. Pat. Nos. 3,125,666, 3,349,213, 2,856,510 and 4,839,489. The disclosed shielding devices provide more complete protection for the molten metal of the weld than a trailer shield device which is separate from the welding torch. However, atmospheric gases may infiltrate the shielding gas and interact with the molten metal if the gas source for the gas shielding/trailer unit is located some distance from the weld surface. A gas shielding apparatus which provides a protective envelope that is substantially impenetrable by atmospheric gases even when the source of the protective stream is spaced from the weld is desirable.
In general, in the disclosed shielding devices separate gas sources are used for the primary shielding cup of the welding torch and the trailer shield. Using separate sources requires that each welding station have two or more sources of inert gas which may be coupled to the welding assembly. The disclosed devices are unsuitable when only one source of inert gas is available. Additional tubes must be used to couple the gas sources to the welding torch and the shielding device. With the second gas source and the multiplicity of tubes, additional work space is required for each welding station. The numerous tubes may restrict the maneuverability of the welding torch. The main supply and the auxiliary supply must both be monitored when welding a workpiece to ensure that the supplies are functioning properly. A gas shielding device which uses a single gas source for isolating and protecting the molten metal of a weld is desirable.
One type of gas shielding apparatus using a single source of inert gas is disclosed in U.S. Pat. No. 5,003,150. The shielding apparatus is formed for the lateral introduction of the stream of gas into a skirted plenum. The skirted plenum is shaped to cover the weld pool and a portion of the weld behind the weld pool, increasing the area protected by the single stream of gas. A gas shielding apparatus which uses a single gas source to form a two or more separate streams of shielding gas is desirable.
The available gas shielding devices are generally complex and difficult to manufacture and install. The complexity increases the manufacturing costs of the devices. Removal of the shielding device from the torch for maintenance, replacement of the electrode, transfer to a different welding torch, and the like may be inconvenient and time consuming. A gas shielding apparatus which may be efficiently and economically manufactured, installed and removed would be particularly valuable.